Weatherable molding composition having improved surface appearance

Abstract

A thermoplastic molding composition which features improved surface appearance is disclosed. The composition contains a blend of (A) a grafted rubber comprising a crosslinked rubber substrate which contains a styrenic core and an acrylate rubber shell, to which grafted is a grafted phase, and (B) a copolymeric matrix containing a copolymer such as styrene/acrylonitrile, and (C) an aromatic (co)polycarbonate resin. The composition is useful in the preparation of molded articles which are characterized in having low haze, high gloss and the absence of corona defect.

What is claimed is:  
     
       1. A thermoplastic molding composition comprising a blend of 10 to 50 wt. % of (A), 0 to 40 wt. % of (B) and 10 to 90 wt. % of (C), where 
       (A) denotes a grafted rubber comprising a crosslinked rubber substrate which contains  
       (A1) about 1 to 50%, relative to the weight of the substrate, of a crosslinked core the crosslinking agent of said core consisting of at least one monomer that contain two or more ethylenic double bonds which are capable of copolymerization and are not conjugated in the 1,3-positions, and  
       (A2) about 50 to 99%, relative to the weight of the substrate of a shell containing at least one polymerized acrylate, to which grafted is  
       (A3) a grafted phase, and where  
       (B) denotes a copolymeric matrix containing a copolymer of at least one monomer selected from a first group consisting of styrene, α-methyl styrene, ring-halogenated styrene and ring-alkylated styrene and at least one monomer selected from a second group consisting of (meth)acrylonitrile, methyl methacrylate and maleic anhydride wherein weight ratio between said monomer of said first group to said monomer of said second group is in the range of 85:15 to about 65:35, and where  
       (C) denotes an aromatic (co)polycarbonate resin, wherein said substrate and said grafted phase relate one to the other, by weight, as 30:70 to 80:20, where (A1) consists of the polymerization product of the crosslinking agent and at least one member selected from the group consisting of styrene, α-methyl styrene, ring-halogenated styrene and ring-alkylated styrene, and where (A2) denotes a crosslinked alkyl acrylate rubber shell enveloping said core, said substrate being present in particulate form having a weight average particle size of about 0.05 to 0.18 microns, and where grafted phase (A3) contains a copolymer of at least one monomer selected from a third group consisting of styrene, α-methyl styrene, ring-halogenated styrene and ring-alkylated styrene with at least one monomer selected from a fourth group consisting of (meth)acrylonitrile, methylmethacrylate and maleic anhydride and wherein weight ratio between said monomer of said third group to monomer of said fourth group is 85:15 to about 65:35 said composition containing no other grafted rubber component.  
     
     
       2. The composition of  claim 1  wherein said grafted rubber (A) is present at an amount of 20 to 40 wt. %. 
     
     
       3. The composition of  claim 1  wherein said copolymeric matrix (B) is present at an amount of 10 to 30 wt. %. 
     
     
       4. The composition of  claim 1  wherein said (co)polycarbonate (C) is present at an amount of 30 to 70 wt. %. 
     
     
       5. The composition of  claim 1  wherein said grafted rubber comprise 40 to 70 percent, relative to its weight, of a crosslinked rubber substrate. 
     
     
       6. The composition of  claim 1  wherein said polymerization product is polymerized styrene. 
     
     
       7. The composition of  claim 1  wherein said shell contains polymerized C 1-18 -alkyl acrylate rubber. 
     
     
       8. A thermoplastic molding composition comprising a blend of 10 to 50 wt. % of (A), 0 to 40 wt. % of (B) and 10 to 90 wt. % of (C), where 
       (A) denotes a grafted rubber comprising a crosslinked rubber substrate which contains  
       (A1) about 1 to 50%, relative to the weight of the substrate, of a crosslinked core the crosslinking agents of said core consisting of at least one monomer that contain two or more ethylenic double bonds which are capable of copolymerization and are not conjugated in the 1,3-positions, and  
       (A2) about 50 to 99%, relative to the weight of the substrate of a shell containing at least one polymerized acrylate, to which grafted is  
       (A3) a grafted phase, and where  
       (B) denotes a copolymeric matrix containing a copolymer of at least one monomer selected from a first group consisting of styrene, α-methyl styrene, ring-halogenated styrene and ring-alkylated styrene and at least one monomer selected from a second group consisting of (meth)acrylonitrile, methyl methacrylate and maleic anhydride wherein weight ratio between said monomer of said first group to said monomer of said second group is in the range of 85:15 to about 65:35, and where  
       (C) denotes an aromatic (co)polycarbonate resin, wherein said substrate and said grafted phase relate one to the other, by weight, as 30:70 to 80:20, where (A1) consists of the polymerization product of the crosslinking agent and at least one member selected from the group consisting of styrene, α-methyl styrene, ring-halogenated styrene and ring-alkylated styrene, and where (A2) denotes a crosslinked alkyl acrylate rubber shell enveloping said core, said substrate being present in particulate form characterized in a bimodal size distribution containing a small mode and a large mode wherein small mode has a weight average particle size of about 0.05 to 0.3 microns, and where the large mode has a weight average particle size of about 0.31 to 1.0 microns and where grafted phase (A3) contains a copolymer of at least one monomer selected from a third group consisting of styrene, α-methyl styrene, ring-halogenated styrene and ring-alkylated styrene with at least one monomer selected from a fourth group consisting of (meth)acrylonitrile, methylmethacrylate and maleic anhydride and wherein weight ratio between said monomer of said third group to monomer of said fourth group is 85:15 to about 65:35.  
     
     
       9. The composition of  claim 8  wherein said shell contains polymerized C 1-18 -alkyl acrylate rubber. 
     
     
       10. The composition of  claim 8  wherein small mode has a weight average particle size of 0.1 to 0.25 microns and where the weight average particle size of the large mode is 0.35 to 0.6 microns. 
     
     
       11. The composition of  claim 8  wherein said grafted rubber (A) is present at an amount of 20 to 40 wt. %. 
     
     
       12. The composition of  claim 8  wherein said copolymeric matrix (B) is present at an amount of 10 to 30 wt. %. 
     
     
       13. The composition of  claim 8  wherein said (co)polycarbonate (C) is present at an amount of 30 to 70 wt. %. 
     
     
       14. The composition of  claim 8  wherein said grafted rubber comprise 40 to 70 percent, relative to its weight, of a crosslinked rubber substrate.